Open-cell metallic structures are widely employed in the aerospace industry and in biomedical applications that require materials to be extremely light as well as strong. In marine infrastructure, however, their usefulness is limited because water quickly fills their interconnected open pores, preventing them from floating even though their bulk density is much lower than that of water.

Engineers in Australia and France have now developed a way around this problem. By combining so-called architected metals with a lightweight polymer foam, they created lightweight, strong, open-cell titanium structures that can float in water, overcoming the density limitation of previous materials while retaining structural performance.

“The innovation opens a new design space for marine structures, vehicles and rescue equipment where we need strength, low weight and buoyancy all at the same time,” says Ma Qian, a materials engineer at the RMIT University in Melbourne who co-led the research.

Beyond Archimedes

According to Archimedes’ principle, an object will float if its effective average density is lower than that of the fluid surrounding it. With open-cell materials, however, it’s more complicated. Because these interconnected frameworks of struts, thin plates or curved surfaces contain interconnected open voids that can fill with water as well as closed voids that cannot, they may fail to float even when their bulk densities (ρ_bulk) are well below that of water.

In the new work, which is detailed in Advanced Materials, Qian and colleagues at RMIT’s Centre for Additive Manufacturing and the Conservatoire National des Arts et Métiers in France developed an alternative measure of density that incorporates only the water-excluding parts of a structure. If the value of this “skeletal density” ρ_skeletal is lower than that of the surrounding liquid, then the structure will float even when water flows through all its interconnected open pores.

The team used this new measure to design a structure based on a recently-developed type of metallic open-lattice metamaterial called a hollow-strut lattice (HSL). Unlike conventional solid-strut designs, HSLs contain millimetre- or sub-millimetre-sized channels within their struts. These channels make them stronger than conventional solid-strut lattice materials of the same density, but that isn’t their only attraction. The presence of such channels also means that materials can be injected into them without compromising the HSL’s open-cell architecture – something that is impossible in traditional structures. Thanks to this feature, Qian explains, appropriately designed hybrid HSLs can float in water while remaining permeable.

Foam and titanium

The researchers made their open-cell hybrid lattice metamaterial by injecting expandable polyurethane (PU) foam, which has a density of 0.08–0.11 g/cm³, into a HSL structure made from a titanium alloy, Ti-6Al-4V.  At the macro level, Qian explains that the foam completely fills the hollow titanium struts, and microscopic analyses reveal continuous, defect-free interfacial bonding between the foam and the inner walls of the struts, while the foam’s own heterogeneous, closed-cell microstructure incorporates pores ranging from ∼10 µm to 200 µm in size. “The closed-cell PU foam limits water ingress into the internal strut channels while the external open-cell architecture remains permeable, so safeguarding marine buoyancy without notable density gain,” Qian says.

The RMIT team submerged both unfilled and foam-filled titanium alloy HSLs in freshwater for more than two months. As expected, all the unfilled HSLs sank when immersed, regardless of strut diameter. The researchers then immersed the materials in natural seawater (which has a measured density of 1.03 g/cm³, slightly higher than the 0.997 g/cm³ they measured for freshwater) over a period of two weeks. They found that the hybrid structures stayed afloat over the experimental period and lost only about 0.15 % of their mass, suggesting they are resistant to corrosion. They also found that the foam-filled HSLs have a higher specific strength than commonly employed marine materials such as high‑density polyethylene and 316L stainless steel.

While the most immediate uses for these new materials will be in seafaring vehicles, lightweight floating structures and rescue equipment, Qian thinks they could have wider applications. “The open-cell architecture allows different materials to be integrated within the same structure,” he tells Physics World. “For example, a biodegradable magnesium scaffold could potentially be combined with a hydrogel containing growth factors for controlled therapeutic delivery during bone regeneration. And in aerospace applications, a hollow-strut titanium lattice might be integrated with a carbon-fibre-reinforced polymer to create lightweight, stiff hybrid structures.”

The researchers now plan to further develop their technology and are seeking collaborations with potential commercial partners. “We want to assess its viability for larger marine applications, including autonomous underwater vehicles and floating platforms and investigate long-term performance under realistic marine conditions,” Qian says. “We also plan to introduce our concepts into our advanced manufacturing and design courses at RMIT to help engineering students and researchers develop new ideas in this emerging field.”

The post Titanium-polymer metamaterial floats in water appeared first on Physics World.

Imagine this. You pick up a contact lens from its container and—yikes!—it falls on the bathroom floor. Before you know it, your cat pounces, claws out. By the time you wrestle it back, the lens looks like a tiny chew toy. And then, just like that—the scratches fade away and the ripped edge seals itself up.

Imagine this. You pick up a contact lens from its container and—yikes!—it falls on the bathroom floor. Before you know it, your cat pounces, claws out. By the time you wrestle it back, the lens looks like a tiny chew toy. And then, just like that—the scratches fade away and the ripped edge seals itself up.

Look closely at Hokusai's The Great Wave off Kanagawa, one of Japan's most iconic masterpieces. The brilliant white of the waves, snow on Mount Fuji and clouds above contain no white pigment. Instead, their whiteness comes from the way light scatters off the unprinted fibers of the washi paper itself.

Look closely at Hokusai's The Great Wave off Kanagawa, one of Japan's most iconic masterpieces. The brilliant white of the waves, snow on Mount Fuji and clouds above contain no white pigment. Instead, their whiteness comes from the way light scatters off the unprinted fibers of the washi paper itself.

 

Arsenic contamination in drinking water poses a critical global public health hazard. Prolonged exposure to inorganic arsenic—predominantly present in groundwater as arsenate, where arsenic exists in its +5 oxidation state—can lead to severe dermatological lesions, cardiovascular diseases, and cancers. To mitigate these health risks, the World Health Organization has established a strict provisional safety guideline of 10 micrograms of total arsenic per liter of drinking water. Because arsenic occurs naturally through the weathering of rocks and minerals in aquifers worldwide, engineering low-cost, scalable, and highly efficient materials for water purification remains a central goal in modern materials chemistry.

Iron-based compounds, particularly iron oxyhydroxides, are among the most effective materials for trapping arsenate. At a fundamental chemical level, arsenate ions readily substitute for surface hydroxyl groups on iron oxyhydroxides, forming strong chemical bonds that permanently anchor the contaminant to the solid surface. However, translating this surface chemistry into practical filters presents a persistent engineering hurdle: maximizing the amount of active iron exposed to water. Simply increasing the iron concentration during material synthesis causes iron nanoparticles to aggregate into large, dense clusters. As these clusters grow, much of the iron becomes buried within the interior bulk, leaving only a tiny fraction accessible at the surface to bind arsenate.

A promising design strategy ¹ overcomes this limitation by decoupling the nucleation of iron particles from their subsequent growth on a flexible, high-surface-area polymer matrix. The foundation of this system is a composite fibrous membrane fabricated from poly(vinyl alcohol) and pectin via electrospinning. In electrospinning, a high-voltage electric field draws a liquid polymer mixture into ultra-fine threads, which solidify into an interconnected, highly porous mesh of nanofibers. Poly(vinyl alcohol) provides structural integrity and water stability upon heat treatment, while pectin—a natural polysaccharide rich in carboxyl and hydroxyl functional groups—serves as a molecular anchor capable of capturing iron ions from solution.

To grow high-density nanostructures without triggering particle agglomeration, a sequential, two-step chemical treatment is applied. First, the electrospun membrane is immersed in a solution containing iron(II) ions (Fe²⁺). The carboxylate groups on the pectin molecules coordinate with these cations, forming uniformly dispersed, nanometer-scale iron seed clusters (~2 nanometers in size) across the nanofiber surfaces as the material dries and oxidizes. In the second step, the seeded membrane is placed in a solution containing iron(III) ions (Fe³⁺). Instead of forming isolated new particles in solution, the newly added iron deposits onto the pre-existing seeds, driving controlled anisotropic growth along preferred crystallographic axes.

This seed-mediated approach yields an extraordinarily high density of surface-exposed iron nanostructures, achieving a 12-fold increase in surface atomic iron content compared to single-step doping methods. High-resolution electron microscopy reveals that these nanostructures adopt an elongated, rice-grain morphology measuring approximately 29 nanometers in width and 110 nanometers in length. Structural characterization using X-ray scattering, X-ray diffraction, and Mössbauer spectroscopy identifies the predominant active iron phase as akaganeite (β-FeOOH), a tunnel-structured, poorly crystalline iron oxyhydroxide known for its exceptional binding affinity toward arsenate.

When evaluated in water purification tests, the nanostructured membrane demonstrates exceptional superadsorbent performance. Using a minimal material dosage of 1 gram per liter, the membrane reduces initial arsenate concentrations from 1000 micrograms per liter down to below 10 micrograms per liter within 24 hours at pH 6, achieving roughly 99% arsenic removal and satisfying WHO safety limits. The material retains high efficiency across a broad operational pH range of 5 to 8, and ICP analysis confirms that iron leaching into the treated water remains safely below 5 micrograms per liter.

Kinetic and isotherm analyses reveal that arsenate removal occurs via surface chemisorption governed by cooperative binding behavior. As initial arsenate molecules bind to active sites on the akaganeite surface, local chemical and electrostatic interactions make adjacent sites even more receptive to further adsorption, resulting in accelerated uptake kinetics. Furthermore, the material performs reliably in complex water environments. Naturally occurring co-contaminants such as fluoride do not interfere with arsenate capture, and the presence of heavy metal cations—such as copper and cadmium—actually enhances arsenate removal by forming secondary surface complexes that create additional binding sites. Although chemical regeneration using sodium hydroxide solution results in a slight decrease in capacity over repeated cycles due to incomplete desorption, the membrane maintains an 81% to 87% removal efficiency, demonstrating strong potential for practical, reusable water remediation systems.

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

The post A polymer membrane that grows its own arsenic-catching surface appeared first on Mapping Ignorance.

A new research project at the New Jersey Institute of Technology is taking a closer look at a strange but important behavior in rubber-like materials: their properties can depend on what happened to them before. With a $125,000 New Directions grant from the American Chemical Society Petroleum Research Fund, chemical and materials engineering professor Gennady Gor and his students will investigate how petroleum-derived polymers absorb fluids, swell, contract and change their elasticity over time. The work could improve predictions of how elastomers perform in everything from industrial seals to oil and gas equipment.

Elastomers are polymers capable of undergoing large, reversible deformations. Silicone, neoprene and natural or synthetic rubber are familiar examples. Their molecular chains can stretch, rearrange and return toward their original configuration, giving these materials their characteristic flexibility. Yet exposure to liquids or vapors can dramatically alter that behavior. Hydrocarbon molecules may enter the polymer network, pushing molecular chains apart and causing the material to expand. At the same time, the absorbed fluid can change the polymer’s stiffness, strength and ability to recover its original shape.

Gor’s project focuses on a phenomenon known as hysteresis, in which a material’s current state depends not only on its present conditions but also on the path it took to reach them. For an elastomer, that means the material may respond differently when it is swelling than when it is shrinking, even if its size and surrounding environment are identical. The difference can arise from molecular rearrangements, delayed relaxation or changes in the interactions between polymer chains and absorbed molecules. Such path-dependent behavior is central to understanding why materials sometimes fail to return fully to their previous mechanical state.

The question is especially relevant for petroleum-related technologies. Elastomers are widely used as O-rings, gaskets and seals because they can deform to fill microscopic gaps and maintain a hermetic barrier. In oil and gas environments, however, these components may encounter complex mixtures of hydrocarbons under pressure and at elevated temperatures. If a seal swells excessively, softens or loses its ability to recover after repeated exposure, it can become unreliable. A better understanding of hysteresis could help engineers select materials and operating conditions that reduce leakage and extend component lifetimes.

The new study represents a shift for Gor’s Laboratory for Materials Interfaces. His previous research has largely examined porous adsorbent materials, which collect molecules on their internal surfaces. Elastomers are different: they do not need pores to take up substantial amounts of fluid. Instead, molecules diffuse into the polymer matrix and interact with its flexible chains. The resulting process is more like a sponge absorbing liquid, although the molecular mechanisms are governed by diffusion, thermodynamics and the elasticity of the polymer network.

Günel Nabiyeva, a fourth-year doctoral student, will lead much of the experimental effort with undergraduate chemical engineering student Elitsa Mileva and second-year doctoral student Supun Rangana. The team has already begun collecting data on how rubber deforms in the presence of liquids and vapors. For Mileva, who has spent considerable time reviewing the scientific literature, the grant will provide an opportunity to move deeper into laboratory work. Nabiyeva describes the project as a new system for the research group because the laboratory has not previously studied elastomers in this way.

The researchers will expose polymer samples to controlled concentrations of hydrocarbon vapors and track how the materials respond. Their measurements will combine swelling, fluid uptake and elasticity rather than treating these properties separately. This approach is essential because a polymer can gain mass and volume while simultaneously becoming softer or, under some conditions, displaying a more complicated mechanical response. Different hydrocarbons may produce different results because their molecular size, chemical structure and compatibility with the polymer influence how quickly they enter the material and how strongly they interact with its chains.

Rangana will contribute expertise in ultrasonic sensing, which can measure subtle changes without physically contacting or damaging the sample. Ultrasonic waves travel through a material in ways that depend on its density, structure and mechanical properties. By analyzing changes in wave transmission or reflection, scientists can detect variations in stiffness and internal condition with high precision. Coupling these measurements to vapor exposure could reveal how quickly elasticity changes as molecules enter the polymer and whether the material follows the same path during desorption as it did during absorption.

The team hopes its results will fill a gap in the fundamental understanding of polymer hysteresis. Although hysteresis is well known in many areas of physics and engineering, relatively few studies have examined how history-dependent elasticity develops in swollen elastomers. The new measurements may help distinguish reversible molecular motions from more persistent structural changes and improve models used to predict polymer performance. Ultimately, the researchers aim to make elastomer behavior less mysterious and more reliable, helping engineers design seals and flexible components that remain dependable across repeated cycles of chemical exposure, swelling and recovery.

Subject of Research: Elastomers, petroleum-derived polymers, polymer swelling, elasticity and hysteresis

Article Title: Ultrasonic Experiments Aim to Reveal Why Rubber Remembers Its History

Web References: Gennady Gor’s NJIT profile; NJIT Laboratory for Materials Interfaces

Image Credits: Courtesy of New Jersey Institute of Technology

Keywords

Elastomers, polymers, hysteresis, rubber, polymer swelling, ultrasonic sensors, materials science, chemical engineering, petroleum research, NJIT

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